The method of repairing the joint portions of existing gas pipes is already well known which employs a repairing device movable inside the pipe. This method is practiced by moving the repairing device inside the pipe to position the device for the joint portion, and then injecting a liquid epoxy resin agent or like sealing agent into the joint portion as sealed from inside the pipe to seal off a gas leak. The repair work for joint portions of existing gas pipes is performed usually over a length of about 50 m to about 100 m as one span, and the joint portions are arranged usually at a spacing of about 5 m to about 10 m. These joint portions are repaired one after another with the travel of the repairing device inside the pipe regardless of the presence or absence of gas leaks.
In practicing the repairing method, there arises a need to form a work opening in the existing gas pipe to be repaired in order to place the repairing device within the gas pipe and to move the device inside the gas pipe for the repair of the joint portions.
The work opening is conventionally formed by partly cutting away the gas pipe, for example, over a length of about 1 m to about 2 m. A terminal tube for accommodating the repairing device therein is installed in the cutaway portion, as connected to the pipe side to be repaired. The terminal tube is provided with a gate valve at each of its inlet side and outlet side so that the repairing device can be inserted from inside the terminal tube into the pipe having the joint portions to be repaired, with the hazard of gas leakage eliminated by alternately opening and closing the gate valves.
However, the conventional method wherein the work opening is formed by partly cutting away the gas pipe requires the following procedures for forming the work opening and restoring the opening portion to the original state.
(i) The repair work for gas pipe joint portions is performed usually over a section of about 50 m to about 100 m as one span, so that an interruption of gas supply over this section will cause inconvenience to many customers who are supplied with the gas from this section. Accordingly, when the gas pipe is to be partly cut away to form the work opening, it becomes necessary to install bypass pipe to ensure the flow of the gas. PA1 (ii) To prevent gas leakage when the pipe is cut away, there arises a need to shut off the gas by inflating a bag within the gas pipe at each side of the cutaway portion as required for various kinds of gas piping work. PA1 (iii) After the terminal tube and the gate valves have been provided in the cutaway portion of the gas pipe at the pipe side to be repaired, the means for shutting off the gas must be removed from the pipe to be repaired in order to insert the repairing device from inside the terminal tube into the pipe. PA1 (iv) After the joint portions have been repaired by the repairing device, the repaired pipe must be blocked with the bag again to shut off the gas for the removal of the terminal tube and the gate valves. PA1 (v) Restoration of the cutaway portion of the gas pipe. PA1 (vi) Removal of the gas shutting off means and the bypass pipe. PA1 forming a work opening in an upper portion of the gas pipe by boring with the gas flowing through the pipe and closing the work opening with a gate valve provided at the work opening externally of the pipe, PA1 connecting a support tube to the pipe at the work opening closed with the gate valve for the tube to extend upwardly of the pipe with the gate valve interposed therebetween, PA1 inserting a guide tube into the support tube in sliding contact therewith through an open upper end thereof, closing the upper open end of the support tube and thereafter opening the gate valve to open the work opening, the repairing device being accommodated within the guide tube so as to be operable by remote control, the guide tube being closed at its upper end and having at its lower portion an outlet for the repairing device to move out of or into the guide tube therethrough as deflected toward a horizontal or vertical direction, and PA1 inserting the guide tube from inside the support tube into the gas pipe through the opened work opening to position the outlet of the guide tube within the gas pipe, PA1 the repairing device being movable from inside the guide tube into the gas pipe through the work opening and the guide tube outlet as positioned within the gas pipe to repair the joint portions, the repairing device being returnable into the guide tube through the opening and the outlet after repairing the joint portions.
As will be apparent from the procedures (i) to (vi), the conventional method requires much labor and time for the formation of the work opening and restoration of the pipe, which result in a longer period and an increased cost for the repair.